Ch. XX.] 



OOLITIC GROUP AND ITS FOSSILS. 



311 



examined by Prof. Owen, who finds that the jaw Fl 's- 8T6 - 



contained on the whole twelve molar teeth, with 

 the socket of a small canine, and three small 

 incisors, which are in situ, altogether amount- 

 ing to sixteen teeth on each side of the lower (^n hl §ltt™e £ ltone& 

 jaw. slate - 



The only question which could be raised respecting the nature of these 

 fossils was, whether they belonged to a mammifer, a reptile, or a fish. 

 Now on this head the osteologist observes that each of the seven half 

 )aws is composed of but one single piece, and not of two or more sepa- 

 rate bones, as in fishes and most reptiles, or of two bones, united by a 

 suture, as in some few species belonging to those classes. The condyle, 

 moreover (b, fig. 375), or articular surface, by which the lower jaw unites 

 with the upper, is convex in the Stonesfield specimens, and not concave 

 as in fishes and reptiles. The coronoid process (a, fig. 375) is well de- 

 veloped, whereas it is wanting, or very small, in the inferior classes of ver 

 tebrata. Lastly, the molar teeth in the Amphitherium and Phascolo- 

 therium have complicated crowns, and two roots (see d, fig. 375), in- 

 stead of being simple and with single fangs.* 



The only question, therefore, which could fairly admit of controversy 

 was limited to this point, whether the fossil mammalia found in the 

 lower oolite of Oxfordshire ought to be referred to the marsupial quad- 

 rupeds, or to the ordinary placental series. Cuvier had long ago pointed 

 out a peculiarity in the form of the angular process (c, figs. 380 and 

 381) of the lower jaw, as a character of the genus Didelphys ; and Prof. 



Fig. 377. 



Tupaia Tana. 



Eight ramus of lower jaw, 



natural size. 



A recent insectivorous mammal from 



Sumatra. 



Fig. SSI. 



Part of lower jaw of Twpaia Tana; 

 twice natural size. 

 Fig. 289. End view seen from behind, showing 



the very slight inflection of the angle at c. 

 Fig. 290. Bide view of same. 



Part of lower jaw of Didelphys Azarce ; 



recent, Brazil. Natural size. 



Fig. 291. End view seen from behind, showing 



the inflection of the angle of the jaw, o, d. 

 Fig. 292. Side view of same. 



* I have given a figure in the Principles of Geology, chap, ix., of another 

 Stonesfield specimen of Amphitherium Prevostii, in which the sockets and roots 

 of the teeth are finely exposed. 



